The present invention relates generally to a resin composition, and more in particular to a filled, flame retardant, resin composition.
Organic resins and especially thermosettable resins, such as unsaturated polyester resins, are finding increasing utility in the preparation of plastic and particularly reinforced plastic molded articles. For example, molded polyester products reinforced with glass fiber have been used successfully in automotive, appliance, furniture, and electrical applications.
In many of these applications, the flammability of the organic resins is an important characteristic. Thus, numerous flame retardant compounds have been incorporated into the organic resins to modify the combustibility of the finished product. Illustrative of such flame retardant compounds are: non-reactive additives such as, for example, halogenated hydrocarbons, phosphates, hydrated alumina, antimony oxide and the like; and halogenated compounds which react with the organic resins and become bound as part of the polymeric matrix. Illustrative of such reactive halogenated compounds are dibromoneopentyl glycol, tetrabromophthalic anhydride, brominated pentaerythritolic polyesters, and the like. The use of reactive halogenated materials as flame retardants in organic resins is described, for example, by J. W. Lyons, "The Chemistry and Uses of Fire Retardants", Wiley Interscience, New York, 1970, pages 370-398.
In addition to a flame retardant, in many applications it is desirable to add inert extenders to displace by bulk at least a portion of the volume of the resin. Such inert extenders, commonly called "fillers," permit the control of density, rigidity, degradability, and cost of the final plastic material. Fillers are extensively used in resin molding formulations where it is unnecessary to maintain transparency in the finished product.
Numerous fillers are commercially available. The most commonly used fillers are calcium carbonate (CaCO.sub.3), clay, short fiber asbestos, talc and alumina trihydrate (Al.sub.2 O.sub.3 .multidot.3H.sub.2 O).
Calcium carbonate may be used at relatively high loading levels with minimum effect on the viscosity of the resin formulation. Moreover, calcium carbonate forms a relatively uniform dispersion throughout the resin, imparts good surface appearance to the finished product, and is a relatively low cost material. However, calcium carbonate contributes little or nothing to the flame retardant or smoke suppressive qualities of the resin composition. In fact, it is thought that the basic properties of calcium carbonate interfere with halogenated flame retardants. Consequently, the simultaneous use of the two components has heretofore been avoided.
Hydrated alumina (Al.sub.2 O.sub.3 .multidot.3H.sub.2 O), also known as alumina trihydrate, is the filler most commonly used when it is desirable to impart flame retardant and smoke suppressive qualities to a filled resin system. For example, the use of alumina trihydrate in reinforced polyester plastics is described in the publication, P. V. Bonsignore, J. H. Manhart, 29th Annual Technical Conference 1974, Reinforced Plastics/-Composites Institute, The Society of the Plastics Industry, Inc., Paper 23-C. However, alumina trihydrate has numerous undesirable properties which detract from its use as a filler. For example, the dispersive properties of alumina trihydrate often yield a nonuniform product with poor molding qualities. In addition, alumina trihydrate can significantly increase the viscosity of the resin formulation. Moreover, alumina trihydrate is also generally more expensive than other commonly used fillers. Finally, the simultaneous use of alumina trihydrate and a halogenated flame retardant has heretofore been thought to significantly increase the smoke generated from a flame-exposed resin system. (See, for example, the publication of Bonsignore and Manhart, supra, p. 3, Table I, Examples 1 and 3.)
It is therefore desirable to develop a cost-effective resin composition which combines the properties of: high filler loading levels; uniform filler dispersion within the resin; satisfactory flame retardant properties, and reduced smoke generation.